The present invention relates to a method for discriminating between tachycardias based on cardiac biopotentials, to a method for discriminating hemodynamically stable and unstable tachycardias based on cardiac signals, and to a method for controlling rate-adaptive pacing based on the simultaneous inputs of signals from multiple physiological sensors.
In particular, the present invention relates to a certain event-based algorithm for discriminating between tachycardias or for controlling rate adaptive pacing.
Event-based systems and methods are new to the field of implantable cardiac treatment systems. The aforementioned co-pending application relates to event-based processing techniques for tachycardia detection and to a method for discriminating between abnormal rhythms and normal sinus rhythm (NSR) using timing interval-binning and averaging, on an event basis.
Like the co-pending application, the invention of the instant application exploits the advantages of an event-based system, but is directed to a different event-based method for analyzing data related to cardiac function.
It is well known in the art that certain tachycardias are more life-threatening than other tachycardias. For example, it is known that ventricular tachycardia (VT) often leads to ventricular fibrillation if not treated, particularly when accompanied by abnormal hemodynamic activity. On the other hand, non-ventricular tachycardia (non-VT) generally does not lead to more threatening conditions. Examples of non-VT are supra-ventricular tachycardia (SVT) and sinus tachycardia (ST). The ability to distinguish the more threatening tachycardias from the less threatening ones is critical in preventing a more serious cardiac condition from developing, such as ventricular fibrillation. It is also desirable to eliminate unnecessary therapy. There are several methods, heretofore known, used for distinguishing between VT and non-VT.
One such algorithm is based upon rate-only. However, the difficulty with this algorithm lies in the fact that the rates of non-VT and VT can overlap. Therefore, it can be extremely difficult to determine the type of the tachycardia based solely on rate.
Another technique, known as A-V timing, compares the timing of atrial and ventricular biopotentials. While this method works better than the rate-only method, problems occur when the atrial and ventricular rates are equal. Specifically, when the ventricular rate is equal to the atrial rate, it is possible that the heart is in a junctional tachycardia, ST, or VT with retrograde 1:1 conduction. In addition, a drawback of this algorithm is its need for two leads for sensing.
Yet another known technique uses a probability density function (PDF) for discrimination on a morphological basis. This method performs well when differentiating narrow versus wide QRS complexes. However, this technique incorrectly identifies narrow monomorphic ventricular tachycardias and cannot be used with a patient with wide QRS complexes, due to preexisting bundle blocks or aberrant conduction, at rest.
In addition, algorithms are known which discriminate hemodynamically stable from unstable tachycardias by examining a single feature derived from cardiac signals (e.g., pressure, volume, or impedance). The majority of these methods rely on right heart measurements. However, any single feature derived from these measurements may not adequately reflect systemic hemodynamic conditions.
Furthermore, algorithms are known which control rate-adaptive pacing by examining a single feature (e.g., stroke volume, dV/dt, pre-ejection interval, minute ventilation, or activity) derived from physiological signals. However, single feature algorithms do not have the sensitivity and specificity required for precise physiologic pacing in all patients.